The invention relates to a method according to the preamble of claim 1. LPC coding has been in wide use for low-cost applications. Therefore, performance to some extent has been compromised. Such methods have often caused a kind of so-called buzzy-ness in the reproduced speech which is represented by certain unnatural sounds that may occur over the whole frequency range and that are experienced by listeners as annoying; the problem also appears in a spectrogram. The state of the art is represented by Alan V. McCree et al, A Mixed Excitation LPC Vocoder Model for Low Bit Rate Speech Coding, IEEE Trans. on Speech and Audio Processing, Vol.3, No.4, July 1995, pp.242-250. Although the reference has taken certain measures to decrease the effects of the buzzy-ness, it was only successive in part.